Variable impedance member for electronic musical instrument



S. HEYTOW July 7, 1970 VARIABLE IMPEDANCE'MEMBER FOR ELECTRONIC MUSICAL INSTRUMENT Original Filed June 7, 1961 2 Sheets-Sheet 1 37 won REPEAT oecm/ Onzcus.

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$oLoMo/v HEVTOW IN VEN TOR ATTORNEY s. HEYTOW 3,519,722

VARIABLE IMPEDANCE MEMBER FOR ELECTRONIC MUSICAL INSTRUMENT July 7, 1970 2 Shets-Sheet 2 Original Filed June 7, 1961 SOLOMON HEvTow HVVENTDR.

ATTORNEY United States Patent US. Cl. 84-117 2 Claims ABSTRACT OF THE DISCLOSURE A manually adjustable impedance member is provided for use in an electrical instrument, and which is used as an adjustable balance control interposed between two tone sources and an output circuit. The impedance member is constructed so that for one-half its span attenuation is provided for one of the sources, but not the other; and so that for the other half of its span attenuation is provided for the second source but not the first. In this manner, at

the mid-point of the adjustment of the impedance member, the signals from both the tone sources are fed to the output circuit substantially unattenuated.

This application is a division of copending application Ser. No. 132,250 which was filed June 7, 1961 now Pat. No. 3,255,294.

The present invention relates to an improved balance means for an electronic musical instrument such as an organ having, for example, a swell keyboard and a great keyboard.

It is an object of this invention to provide an imporved balance means under the selective control and adjustment of the performer through which the volume of sound controlled by the swell keyboard of the organ and by the great keyboard of the organ may be relatively adjusted in the speaker or other transducing of the organ; and wherein at the mid-point or mid-region of such adjustment both keyboards apply substantially maximum volume output to the transducing system.

The variable impedance member of the present invention may be employed in an electronic organ having tone generators for producing the various pitches of a scale, such as a tempered scale. The audio frequencies from the tone generators are applied to keyboard switching circuits, illustrated in the present case as consisting of a swell keyboard and a great keyboard. From each of the keyboards the tones are fed to formant or voicing circuits wherein the timbre of the tone is altered or selected in accordance with the voicing tabs, which are set at the console by the organist.

It is a feature of the present invention that one of the keyboards, in this case the swell keyboard, has its formant circuits divided into two major categories, one accommodating the flute or pure tones and the other accommodating the more complex tones, sometimes known as the string formants (although this also comprehends the various wind and percussion instruments which generate complex tones in contrast to the relatively pure tones of the flute family).

In accordance with the present invention the tones from the swell complex formant circuits and from the swell flute formant circuits may be conveyed over two separate tone paths to the tone output system, which usually consists of an amplifier and loudspeaker, but may consist of any transducing means such as a transmission line, recording head, or other suitable circuit or system for employing the tones received. The two paths are so arranged that one goes directly to the tone output system without per- 3,519,722 Patented July 7, 1970 cussion, while the other is sent through a modulating means which normally block transmission of the tones except when a modulating pulse is applied thereto from a suitable pulse means. The pulse means may be activated from triggering pulses received from the swell keyboard keys upon each actuation of a key. Such a percussive modulating circuit is illustrated by way of example in pending application Ser. No. 669,112, filed July 1, 1957, entitled Percussion Circuit, Stanley Cutler et al., to which reference is made for enhanced understanding of the present specification.

In accordance with the present invention, the pulse means includes a multivibrator and shaper which pulse modulates the tones passing through the percussion path of the organ and which may be selectively adjusted by the performer to produce either iterative or reiterative percussion. By iterative percussion is meant a percussion wherein with each depression of the key in a keyboard (in this case the swell keyboard) the tones corresponding to all keys which are depressed at that particular moment, and which are applied to the modulator by the formant and other switching circuits, will be sounded in percussed form. To achieve this the multivibrator is connected so as to operate as a monostable or one shot device, delivering a single pulse for each triggering impulse applied thereto from the swell keyboard circuit. Reiterative percussion as used herein is achieved by connecting or switching the multivibrator so as to be an oscillator or free running device, which delivers repeated output pulses, completely independent of any input thereto. In accordance with the present invention the oscillator or repeat frequency of the reiterative percussion maybe adjustably controlled by the performer.

Preferred forms of the present invention will now be described with reference to the accompanying drawings wherein;

FIG. 1 is a fragmentary plan view of an organ console showing particularly the voicing and percussion controls;

FIG. 2 is a wiring diagram partly schematic illustrating the circuitry of the present invention; and

FIG. 3 illustrates a modified form of a portion of the circuit of FIG. 2.

Referring to FIG. 1 the plan view of the console illustrates the left hand portion of a swell keyboard 14 and below it the left hand portion of a great keyboard 15. Generally aligned with the swell keyboard 14 and lying immediately to the left are voice or timbre controls manually operable by the performer, some of which are conventional and some of which are unique to the present invention.

Numeral 5 represents rockable tabs which control, for the most part, the various voicing or format circuits, to

' apply the desired timbre to the tones applied to the the present invention, the flute tabs 20 are colored one distinctive color, for example gray, while the complex tabs 18 are colored another distinctive color-,for example red.

In the second line of tabs, the group of tabs 17 control the voicing circuits for the great keyboard 15.

Numeral 6 represents rotatable knobs which control respectively vibrato rate, vibrato depth, and pedal volume including the on/ofl? switch for the organ. Numeral 27 is a manual balance control for controlling the relative volume of sound applied to the speaker from the swell, and great keyboards, respectively. A special balance control is employed in accordance with the present invention whidh will be described hereinafter.

Numeral 90 is a two position tab which simply determines whether or not percussion will be sounded. The tab 90 controls a multi-pole two position switch to selectively switch the tones delivered by the various voicing circuits and by the percussion modulator, as will be described hereinafter. Tabs 7 control the voicing of the pedal circuit, while tab 8 is an on/olf switch controlling the use or non use of vibrato.

Aligned with and to the left of the great keyboard is the control panel for the unique percussion combinations. Knob 85 serves to continuously vary the repeat rate or oscillation frequency of the multivibrator which produces the reiterative percussion, independent of any key actuation. This control becomes effective when the knob 35 is moved to its repeat position. The knob 35 controls a two-pole, four-position switch, one position of which is repeat as mentioned above, and the other three of which serve to control in discrete steps the decay time of the percussion pulse applied to the modulator means; this serves to control the duration of the pulse envelope. Knob 100 controls a three-pole, five-position switch, which selectively switches the tones from the tone generator and formant circuits, in various selected combinations, to the transducer or to the input of the percussive modulator. By judicious use of these five positions, the performer can achieve an extremely wide variety of tonal effects simulating not only individual instruments, but also a plurality of concurrent discrete instruments actuated by a single key of a keyboard, in this case the swell keyboard.

Referring to FIG. 2, a diagram illustrating the device of the invention as incorporated into an electronic organ is shown. Tone signals are generated in a tone generating system 11 which may comprise a plurality of electronic oscillators. The various tone signals are fed to respective associated switching circuits in the swell keyboard circuits 14 and the great keyboard circuits 15. Tone signals are selectively fed from the great keyboard circuits 15 to the great voicing networks 17 in accordance with the actuation of the keys of the great keyboard. Similarly tone signals are fed from the swell keyboard circuits 14 to the swell complex voicing networks 18 and the swell flute voicing networks 20, in accordance with actuation of the keys of the swell keyboard. The various voicing networks comprise electrical formant filters which are used to shape the tone signals by techniques well known in the art, to produce various timbres.

The variously filtered signals are fed from voicing networks 17, 18 and 20 to selector switches 22, and thence selectively to percussion modulator and manual balance control 27. The signals from selector switches 22 retain their voice identity as great and swell signals. Manual or keyboard balance control 27 comprises an attenuating and mixing pad which is used to mix the great and swell inputs and vary their relative amplitudes. The output of manual balance control 27 is fed to amplifier 30 where it is appropriately amplified and fed to loudspeaker 32. Elements 30 and 32 are representative of any suitable tone output system which may include other transducers such as recording heads or may simply be a transmission line.

The keys of the swell keyboard are connected in a pulse generating circuit so that when any key is actuated, an output pulse is generated. Output pulses 36 from the swell keyboard circuits 14 are fed through switch 35, when it is in the position shown, to a pulse means including a percussion multivibrator 37 and a shaping means 45. Percussion multivibrator 37, with switch in the position indicated, operates as a monostable or one shot device and generates a generally rectangular pulse 40, in response to pulse input signals 36 from the swell keyboard circuits.

Pulse 40 is fed from multivibrator 37 to the shaping circuit or network where it is employed to charge an RC time constant network, having an adjustable decay 4 time. The output pulse 63 from the network is applied as a modulating pulse to the modulator 25. There it amplitude modulates the continuous tone 105 applied as a carrier to the input 48 of a modulator 25 and produces a shaped burst of percussed tone 101 at the output 47 thereof. The sustained tone 105 at the input to the modulator 25 is substantially blocked except when a pulse 63 is applied at 99 to pass the tone 101. It will be noted that the envelope of the tone 101 substantially corresponds to the shape of the input pulse 63. This burst 101 is a percussive pulse, in that it simulates quite closely the timbre of various and sundry percussive instruments,

1 as will be explained more fully hereinafter.

The output 101 of modulator 25 is fed to selector switches 22 from where, with percussion in use, it is coupled to the swell line 96 running to manual balance control 27.

Switch 35 may alternatively be placed in any of four positions, as shown, at the election of the operator. When switch 35 is in the first or upper position, percussion multivibrator 37 operates as an oscillator or free running device at a preselected repetition rate. In this position feedback is provided between the multivibrator stages to achieve the desired free running operation. The details of the operation of the multivibrator will be explained hereinafter. Switch 35 thus provides means for alternatively connecting the multivibrator as a monostable, or one shot device operating in response to keys in the swell keyboard circuits 14 or alternatively as a free running device, or oscillator.

Stages of multivibrator 37 are so biased that with switch 35 in the position indicated in FIG. 2, and with no output signal from the swell keyboard circuits 14, transistor 51 will continually conduct while transistor 50 is cut off. With the actuation of any of the keys of the swell keyboard, a negative output pulse 36 is fed from the swell keyboard circuits 14 to fixed contacts b, c and a of switch 35. With the upper movable contact arm of switch 35 in contact with fixed contact b, c or a, pulse 36 is fed to the base of transistor 51, driving this transistor to cutoff. When transistor 51 is driven to cutoff the voltage at its collector rises to the B plus supply voltage (plus 10 volts). This positive going signal is fed through capacitor 55 to the base of transistor 50', and drives this transistor into the conductive state. The positive going signal appearing at the collector of transistor 51 is also coupled through diode 57 to capacitor 59 in shaping network 45. Across capacitor 59 is a resistive network which includes a bias control resistor 61 returned to B minus (minus 5 volts). With the arms of switch 35 in the c and 0' position, capacitor 70 is added to the R/C discharge circuit to increase the time constant of the circuit and hence the time duration of the output pulse 63 to a medium range. The time duration of output pulse 63 may be increased to a long range by switching the arms of switch 35 to the d and 0! positions to connect capacitor 73 into the R/C discharge circuit. Capacitor 73, of course, must have a substantially greater capacitance than capacitor 70 to achieve the desired end result. If desired the switch may be arranged so that the capacitance of 73 is added to that of 70, at the d position, thereby reducing cost of components. This is done by well known switching techniques which are old in the art.

With the movable arms of switch 35 is the a and a positions, a feedback path is provided from the collector of transistor 50 through resistor 78, capacitor and switch 35 to the base of transistor 51. This feedback causes the multivibrator to operate as a free running device or oscillator at a frequency determined by the R/C time constant of the circuit, the supply voltage and the characteristics of transistors 50 and 51. This oscillation frequency can be varied by means of potentiometer 85.

Switch 35 is thus utilized to operate the multivibrator as a single shot device in response to the pulse output 36 of the swell keyboard circuits 14 or as a free running device with a repetition rate which can be adjusted by means of potentiometer 85. In the three lower positions of the switch 35 the one shot mode of operation is employed with three different pulse widths or durations for the pulse 63 delivered by the network 45.

Tone input signals 105 are fed from selector switch 100 via line 48 to the primary winding of transformer 65 in modulator 25. These signals are inductively coupled to the secondary winding of this transformer so that they appear at the bases of transistors 107 and 108. The output pulse 63 from the pulse means 37, 45 is fed via line '99 to the center tap of the secondary winding of transformer 65 so that it also appears at the bases of transistors 107 and 108. Transistors 107 and 108 are so biased that they will only conduct when the modulator output pulse 63 appears at their bases. Transistors 107 and 108 thus act as gates which conduct only during the times when pulse 63 is present. The signals which are gated through transistors 107 and 108 are coupled from the primary of transformer 110 to its secondary. The output 101 of the percussion modulator 25, which is a modulated tone signal having an envelope corresponding to the modulation pulse 63, is fed via line 47 to movable arm e of percussion switch 90. With the percussion switch in the on position, which is the position indicated in FIG. 2, the modulated output signals are fed via arm e to the swell output line 96 which runs to manual balance control 27. The output of manual balance control 27 is amplified in amplifier 30 and then fed to loudspeaker 32.

The multivib'rator 37 and the pulse shaping network circuit 45 thus constitute in conjunction a pulse means for producing and delivering a suitable modulating pulse 63, which opens the modulator 25 and forms the envelope for the tone output 101.

The outputs of the great voicing network 17, the swell complex voicing network 18, and the swell flute voicing network 20 are fed to movable arms 1, g and h respective ly of percussion switch 90. With percussion switch 90 in the on position, the movable arms e, f, g and h of the switch are connected as shown in FIG. 2 to feed the output of great voicing network 17, swell complex voicing network 18, and swell flute voicing network 20 to movable arms k, i and 1 respectively of selector switch 100.

With the percussion switch 90 in the on (down) position, movable arm e feeds the output 101 of modulator 25 to swell output line 96 which is connected to the swell input terminal of manual balance control 27. With percussion switch 90 in the off (up) position, the output 101 of the modulator is dead ended at switch arm e; the output of the great voicing network 17 is fed through arm 1 to the great output line 95 which runs to manual balance control 27, and the outputs of the swell complex voicing network 18 and the swell flute voicing network 20 are both fed to the swell output line 96 which runs to manual balance control 27.

With switch 90 in the bit position, the switch 100 is ineffective and its position is of no moment.

With the percussion switch 90 in the on position, the movable arms 1', i and k of selector switch 100, which are ganged together, may be positioned to any one of the five contact positions as shown in FIG. 2 to selectively couple the great voicing network, swell complex voicing network, and the swell flute voicing network and various combinations thereof to either the input winding of transformer 65 in modulator 25 or to the great and swell output lines 95 and 96. Thus, a great variety of percussive and unpercussive signals can be produced.

It will be noted that the percussion control switch 100 has five positions selective at the will of the performer. In FIG. 2, starting from the top, the first position is denominated All swell. This signifies that both the complex and the fiute tones from the swell manual will be percussed by being directed through the modulator 25,

while the gerat manual will be unpercussed. This is confirmed by noting that tones from the swell complex and swell flute formant circuits 18 and 20 pass through the switch arms g and h, thence to the arms i and 1', respec-: tively, and thence to the input line 48 of the modulator 25. Tones from the great manual circuit 17 on the other hand go through the switch arm 1 to the switch arm k and thence to the great output line 95. The percussed swell tones emerge from the modulator 25 on the line 47, pass through the arm e and thence to the swell output line 96. Tones on the lines and 96 are then applied to the manual balance control 27 and thence to the common output line 49 feeding the amplifier 30.

The second position of the switch 100 is denominated Swell red. This indicates that only the red or complex tones of the swell manual will be percussed. The grey or flute tones of the swell manual will be unpercussed; and the great manual will also be unpercussed. Thus it is seen that in this position the swell flute tones from 20 pass through arms h and j, thence through attenuating resistor 111 and to the swell output line 96. Swell complex tones from 18 pass through arms 1' and i to the modulator line 48, thence through the modulator and to the arm e and swell output line 96.

The third position of the switch 100 is denominated Swell grey. In this position, the grey or flute tones from the swell manual are percussed, while the red or complex tones are unpercussed. The great manual is, as before, unpercussed. This may be readily seen by tracing the switch positions in the manner exemplified above.

The fourth position of the switch 100 is denominated Great to Swell. In this position of the switch very unique effects can be achieved in that the modulator 25 receives only tones from the great voicing network 17, but since the pulsed output 101 of the modulator 25 is under the control of the output pulse 36 from the swell keyboard 14, it follows that percussed great tones will appear at the output, but only at the moment of depression of a key in the swell key-board 14. This assumes, of course, that the switch 35 is in one of its three iterative positions. If the switch 35 is in its reiterative or repeat position a, then the percussive pulses 40 and 63 are independent of the keyboard 14 and run freely as explained hereinbefore. Assuming that the switch 35 is set for one of the three iterative percussion positions, the performer may hold a note or chord depressed in the great keyboard but no sound will emanate except when a key in the swell keyboard is depressed. When such occurs, the depressed notes of the great keyboard will sound percussively through the output system, and simultaneously whatever tones from the swell keyboard as have been selected by the swell voicing tabs 18, 20 will be sounded in sustained fashion.

Finally the fifth position of the switch 100 is denominated Great and Swell. In this position all tones from all of the voicing circuits 17, 18 and 20 will be percussed and no sustained tones will be applied to the output circuit. Here again, however, the application of the percussive envelope will be dependent on the depression of a swell key 14 (assuming switch 35 in iterative position), so that the mere depression of a note or chord in the great keyboard will not necessarily sound those particular tones; the actual sounding of great tones is dependent upon the coincidence of depression (sustained or momentary of the desired key in the great keyboard plus any key in the swell keyboard.

It will be noted that in the last two positions of switch 100, since the tones of the great keyboard pass through modulator 25, they do not appear on the great output line 95, but instead appear, along with any swell tones, on the swell output line 96. This renders the control 27 ineffective as a balance control or mixer and makes it a simple attenuator for the swell line 96.

From the above description it will be noted that the positions two and three of switch 100, depression of a single key in the swell keyboard 14 may cause the'sounding of apercussed tone of one timbre and an unpercussed or sustained tone of another timbre. While both of these tones will correspond to and be actuated by the particular swell key depressed, they need not necessarily be of the same pitch. This will depend on the swell tabs 18 and 20 which are actuated at the time. For example, if among the tabs 20, there is in the on position, the swell flute quint /3, and among the tabs 18, the clarinet 8' and if the switch 100 is in the second position, the 8 clarinet note will come through with clarinet timbre and percussed, while the 5 /3 flute note will come through unpercussed. The 8 note is of the pitch corresponding exactly to the depressed key; however, the 5 /3 note is (in accordance With regular organ practice) of a higher pitch, being a fifth interval above the pitch of the depressed key. Both notes however will be sounded simultaneously, one'unpercussed and the other percussed, upon depression of a single given key in the swell keyboard. I The manual balance control 27 is comprised of a pair of attenuators in the form of impedances or resistors 210 and 211, made adjustable by sliders 212 and 213 respectively. The resistors are shown in circular form because as a practical matter it is simpler to provide a rotatable adjusting knot than a linearly slidable tab; but the physical disposition on the parts is immaterial to the function. In terms of the path of movement or adjustment of the sliders 212 and 213, which are ganged together as shown at 214, each attenuating impedance consists of two portions. The first portion of the impedance 211, which is in the swell circuit line 96, consists of a negligible impedance conductor 216; it is connected to and followed by an appreciable resistance portion 217, which forms the second portion. Thus, in the first half or portion of its clockwise movement, the slider 213 does not markedly change the impedance or attentuation introduced into the sWell line 96. It is only when the slide 213 engages the portion 217, that the attenuation begins to steadily increase.

The impedance 210 in the great keyboard line 96, is arranged in opposite fashion. That is to say, in the first portion of the clockwise movement of its slider 212, the resistance 210 has an appreciable value illustrated at 218, while in the last or second portion of the movement of the slider 212, there is substantially a very low impedance conductor 219. It will be noted that this is exactly the complement of the arrangement for the impedance 211. It will be further noted that since the sliders 213 and 212 are ganged together, at one point (substantially the mid point in the adjustment thereof) the impedance introduced into the line 96, is negligible as is also the impedance introduced into the line 95. Thus at the mid point of the manual balance control 27, substantially the full volume output from both the swell line 96 and the great line 95 isapplied to the amplifier 30. From this point, moving clockwise, there is introduced a steadily increasing attenuation or impedance into the swell line 96, as the slider 213 traverses and encompasses an increasing portion of the resistor 217, while substantially no attenuation is introduced into the great line 95, since the slider 212 slides over the negligible resistance conductor 219. Conversely, moving counter clockwise from the mid point introduces steadily increasing impedance and attenuation into the great line 95 as the slider 212 encompasses an increasing portion of resistor 218, while substantially no attenuation is introduced during this traverse into the swell line 96.

The advantage of this structure is that while the full range of balance between the two manuals is available to the performer, he also has available at the mid-point of the adjustment, the full volume output of both manuals.

The circuit described makes possible a wide variety of instruments and instrument combinations, with remarkable similitude, for example, banjo, bagpipe, harpsichord, vibraharp, calliope, zither, marimba, chimes, Hawaiian guitar, piano and glockenspeil, piano and celeste, musette and temple blocks, clarinet and marimba, flute and mandolin, boogy woogy, calliope and banjo.

One of the more striking effectsHawaiian guitaris to be found, for example, by placing switch in the second or swell red position, with the decay 35 set to medium or long (0 or d). The effect produced is the sharp (percussive) twang of the plucked strings, which dies away while the smooth melody of the flute lingers on. This transition of tones gives the illusion of the familiar slur of this guitar. As reference to FIG. 2 will show, this is done by causing a flute tone, for example, the 4 flute from the network 20, to pass unpercussed to the output line 96, while complex tones, for example, the 8 clarinet and 8 oboe, are percussed through the modulator 25 before application to the output line 96.

This effect may, if desired, be enhanced by inserting in the output line 47 from the modulator 25, a phase invertor 201, which simply inverts the phase of the percussed tones before they are recombined with the unpercussed tones at the output line 96. The initial attack volume of the percussed tone, may be set appreciably greater than the volume of the unpercussed tone. Thus as the percussed tone dies out, and approaches the volume of the unpercussed tone, the phase inversion actually causes a substantial cancellation of the fundamental of the tone, with a resulting apparent momentary lowering of the volume, before it comes back up and continues With the drawn out slur effected through the flute alone. This simulates strikingly the Hawaiian guitar effect achieved by the bar in the hands of a skilled guitar player.

Other interesting effects derivable from the swell manual alone and by actuation of a single key, are as follows. Mandolin combined with flute is achieved by setting the voice tabs 20 for the 8 flute and the voice tabs 18 for the 8' oboe and 8 violin. Switch 100 is set in the second or swell red position while the decay switch 35 is set at the first or repeat percussion position. The repeated percussion simulates the mandolin, since the red tabs 18 are percussed, while the 8 flute comes through unpercussed.

Wood blocks with clarinets is achieved by setting the grey (flute) tabs 20 at 4 flute and 5 /3 flute and the red (complex) tabs 18 at 8 clarinet. Switch 100 is set at the third or swell grey position and the decay switch 35 is set at the short decay position b. Each depression of a single key in the swell keyboard 14 causes the two flute tones (4' and 5 /3) to be percussed with short time decay, While the 8 clarinet tone comes through unpercussed and is sustained as long as the note is depressed. A striking duet between wood block and clarinet is thus achieved entirely from the swell manual. This is an excellent example of where the two tone paths, one percussed and the other unpercussed, do not even carry notes of the same pitch, in view of the fact that the two flute tones are respectively an octave and a fifth above the pitch of the sustained clarinet tone.

Calliope with banjo is achieved by employing the 8' flute and the 8' oboe, with switch 100 in the second or swell red position, and switch 35 in the a or repeat position. The 8 oboe is passed through the percussive tone path at a fairly rapid repeat rate to simulate a banjo, while the 8' flute is passed through the unpercussed or sustained tone path to simulate the calliope.

In FIG. 3 there is shown an alternative form which the modulator may take. This is shown at 25' wherein the input 48 and output 47 lines are coupled simply by a light sensitive resistor 230 having the property that when not illuminated, the resistance or impedance is very high, dropping markedly in response to illumination thereon. A suitable optical system, represented schematically by the lens 231, is used to illuminate the resistor 230 from a source of illumination such as a light bulb 232. The light bulb is energized by the modulating pulse 63 applied to the input line 99 and preferably amplified as shown at 233.

In this form of modulator the resistance of 230 is caused to change inversely with the magnitude of the pulse 63 and thus in eifect open the gate between the input and output lines 48 and 47, in substantially the same way as the modulator 25 shown in FIG. 2.

The impedance 230 is a type known in the art generally as a light sensitive impedance or light determining impedance and having the properties set forth hereinbefore.

The device of this invention thus provides a simple yet highly eflYective percussion circuit having a versatility of operation and incorporating a capability of producing a repetitive percussion signal at a preselected repetition rate. The repetitive percussion signal can be used to produce a strumming effect at a precise and regular rate. This can be used both to instill a sense of rhythm in the novice and to facilitate the playing of accompaniment and solo etfects for a more experienced musician.

While the instant invention has been shown and described herein in what is conceived to be the most practical and preferred embodiments, it is recognized that departures may be made therefrom within the scope of the invention which is therefore not be limited to the details disclosed herein but is to be afforded the full scope of the claims.

I claim:

1. In an electrical musical instrument, first and second tone sources for producing tone signals, a common output system for the tone signals from said first and second tone sources, and an adjustable balance control serially interposed between said first and second tone sources and said output system and comprising first adjustable attenuating means including a first impedance connected to one of said tone sources and second adjustable attenuating means including a second impedance connected to the other of said tone sources, first and second sliders respectively contacting said first and second impedances and connected to said common output system, said sliders being ganged together for simultaneously adjusting said first and second attenuating means, said first and second impedances each having a nonlinear relationship between the attenuations and the adjustment of the respective sliders such that substantially one-half of the span of said adjustment produces substantially no impedance change in one of said attenuating means While producing substantial and continuous impedance change in the other of said attenuating means, and the other half of the span of said adjustment producing substantially continuous impedance change in said one attenuating means while producing substantially no impedance change in the other of said attenuating means.

2. The combination defined in claim 1, in which the value of each of said impedances is essentially zero at the mid-point of said adjustment so that the tone signals from both of said tone sources are fed to said common output system substantially unattenuated at such midpoint of said adjustment.

References Cited UNITED STATES PATENTS 2,573,122 10/1951 Weber.

3,036,158 5/1962 Romano.

FOREIGN PATENTS 1,083,867 6/1960 Germany.

844,126 8/ 1960 Great Britain.

HERMAN KARL SAALBACH, Primary Examiner MARVIN NUSSBAUM, Assistant Examiner U.S. c1. X.R. 84-1.19; 333 s1 

